B-cyclodextrin derivatives and their use against anthrax lethal toxin

ABSTRACT

The invention provides low molecular weight compounds that block the pore formed by protective antigen and inhibit anthrax toxin action. Structures of the compounds are derivatives of β-cyclodextrin. Per-substituted alkylamino derivatives displayed inhibitory activity, and they were protective against anthrax lethal toxin action at low micromolar concentrations. Also, the addition of one of the alkylamino derivatives to the bilayer lipid membrane with multiple PA channels caused a significant decrease in membrane conductance. Thus, the invention also provides methods for protection against anthrax toxicity.

This application claims priority to U.S. Provisional Application No.60/539,577, filed Jan. 29, 2004.

This work was supported by grant 1R43AI052894-01 from the NationalInstitute of Allergy and Infectious Diseases. The government has certainrights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to protection against Anthrax-mediatedbiotoxicity.

2. Summary of the Related Art

Bacillus anthracis is one of the most dangerous potential biologicalweapons. Currently, there is no effective treatment for inhalationalanthrax, beyond the administration of antibiotics shortly afterexposure. Time delay reduces the effectiveness of antibiotic treatment.Dixon et al., Anthrax. N. Engl. J. Med.: 341, 815-826 (1999) teachesthat major factors playing a role in anthrax infection are the cytotoxiceffect of anthrax toxin, and bacteremia leading to oxygen andnutritional substance deprivation, accumulation of various bacterial andhost toxic products with eventual organ failure and death.

Brossier et al., Toxicon. 39: 1747-1755 (2001) teaches that the twoanthrax toxins are formed by three different proteins: protectiveantigen (PA) which either combines with lethal factor (LF) to formlethal toxin (LeTx), or with edema factor (EF) to form edema toxin(EdTx). LF and EF are enzymes targeting substrates within the cytosol,and PA facilitates their transport across the cell membrane forming aheptameric pore. PA assembles into a ring-shaped heptamer with anegatively charged lumen and exposes a hydrophobic surface for bindingof LF and EF. Petosa et al., Nature 385: 833-838 (1997) teaches thethree-dimensional structure of the PA pore.

Karginov et al., FEMS Immun. Med. Microb. 40: 71-74 (2004) teaches thattreatment of Bacillus anthracis infected mice with a combination of theantibiotic ciprofloxacin and partially purified antibodies againstanthrax protective antigen dramatically increased survival rates incomparison with antibiotic treatment alone.

Although promising, antibodies are less attractive as potential drugs incomparison with low molecular weight compounds, which offer potentiallybetter penetration through membranes and are not sensitive to proteases.

Therefore, there is a need for new safe and efficient treatments tosupplement to traditional antibiotic intervention.

BRIEF SUMMARY OF THE INVENTION

The invention provides new safe and efficient treatments to supplementto traditional antibiotic intervention.

In a first aspect, the invention provides low molecular weight compoundsdesigned to block the pore formed by PA, which can inhibit anthrax toxinaction. The high-affinity blockers of PA according to the invention arederivatives of beta-cyclodextrin (β-CD), which is a cyclic moleculecomprising seven D-glucose units and having sevenfold symmetry, like thePA pore.

In a second aspect, the invention provides methods for inhibiting thetoxic effects of Bacillus anthrasis. The methods according to thisaspect of the invention comprise contacting a cell with a compoundaccording to the first aspect of the invention.

In a third aspect, the invention provides novel methods for makingcertain derivatives of —CD.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows embodiments of compounds according to the invention.

FIG. 2 shows protection of RAW 264.7 cells from LeTx-induced cell deathby β-CD derivatives.

FIG. 3 shows inhibition of cytopathic effect of LeTx expressed aspercentage of the LeTx effect induced in cells not treated withinhibitor.

FIG. 4 shows typical tracks of ion conductance for PA channelsreconstituted into planar lipid membranes. The downward arrow indicatesthe addition of PrAmBC to the cis side of the membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to protection against Anthrax-mediatedbiotoxicity. The invention provides new safe and efficient treatments tosupplement to traditional antibiotic intervention. The references citedherein reflect the level of knowledge in the field and are herebyincorporated by reference in their entirety. In the case of a conflictbetween the teachings of the cited references and the presentspecification, any such conflict shall be resolved in favor of thelatter.

In a first aspect, the invention provides low molecular weight compoundsdesigned to block the pore formed by PA, which can inhibit anthrax toxinaction. The high-affinity blockers of PA according to the invention arepreferably derivatives of beta-cyclodextrin (β-CD), which is a cyclicmolecule comprising seven D-glucose units and having sevenfold symmetry,like the PA pore. Alternatively, molecules similar to β-CD, cyclicmolecules having sevenfold symmetry, like the PA pore may be used. Theoutside diameter of β-CD—15.3 Å—is comparable with the diameter of thePA channel lumen, which is 20-35 Å according to X-ray analysis data, andabout 12 Å at its most narrow point according to the measurement ofcurrent flow through the channel. Alternative cyclic molecules should beof similar size.

Preferred derivatives of β-CD include hepta-6-alkylamino derivatives ofβ-cyclodextrin. β-CD substituted with positively charged groups ofvarious sizes because the lumen of the PA pore is mostly negativelycharged. Also, the positively charged groups might alter the local pHinside the lumen, inhibiting the conformational change required for theformation of the transmembrane channel.

Preferred compounds have the formula

wherein R₂ is H, OH, OAc, OMe, or O(CH₂CH₂O); R₃ is H, OH, OAc, OMe,OSO₃Na, or NH₂; and R₆ is H, NH₂, SCH₂CH₂NH₂, SCH₂CH₂CH₂NH₂,SCH₂CH₂CH₂CH₂NH₂, I, N₃, SH, lower alkyl, S-alkylguanidyl,O-alkylguanidyl, S-aminoalkyl, O-aminoalkyl, aminoalkyl, aralkyl, aryl,heterocyclic ring(s), or OSO₃Na. Most preferably, R₆ is H, NH₂,SCH₂CH₂NH₂, SCH₂CH₂CH₂NH₂, or SCH₂CH₂CH₂CH₂NH₂.

For purposes of the invention, the term “lower alkyl” means an alkylgroup from 1 to 7 carbon atoms. The terms “alkyl” and “aryl” includealkyl or aryl groups which may be substituted or unsubstituted.Preferred substitutions include, without limitation, substitution withnitrogen containing moieties, including amino groups, which may be monoor disubstituted, preferably with alkyl or aryl groups. Also, forpurposes of the invention the term “alkyl” includes chains of 1-7 atomswith one or more nitrogen atoms and the remainder carbon atoms.

Particularly preferred derivatives of β-CD are shown in FIG. 1.

In a second aspect, the invention provides methods for inhibiting thetoxic effects of Bacillus anthrasis. The methods according to thisaspect of the invention comprise contacting a cell with a compoundaccording to the first aspect of the invention. Preferably, the cell isin a mammal, most preferably in a human.

The four hepta-6-alkylamino derivatives of β-cyclodextrin suggested byour structure-based evaluation were synthesized. These and some otherβ-cyclodextrin derivatives synthesized by us or obtained elsewhere (FIG.2) were tested for their ability to inhibit cytotoxic effect of LeTx onmouse macrophage-like cells RAW 264.7.

Surprisingly, only the alkylamino derivatives originally suggested basedon structure-based design, displayed inhibitory activity, and they wereprotective against LeTx action at low micromolar concentrations (FIG.3). These experiments also showed that the compounds were not toxic toRAW 264.7 cells up to 25 μM concentration, while their IC₅₀ were as lowas 4.4 μM (FIG. 3). The rest of the compounds presented in FIG. 1displayed no inhibitory activity at concentrations 100 μM and lower.

One of the alkylamino derivatives—PrAmBC—was tested for the ability toblock ion conductance through PA channels reconstituted into planarbilayer lipid membranes. It was demonstrated that the addition of PrAmBCto the bilayer lipid membrane with multiple PA channels (about 60)caused a significant step-like decrease in membrane conductance at 3 nMconcentration of the compound (FIG. 4).

Persubstituted β-cyclodextrin derivatives can potentially also beutilized for blocking of other toxins that form heptameric transmembranechannels, such as staphylococcal α-hemolysin. Derivatives of hexamericα-cyclodextrin may also find utility against targets such asHelicobacter pylori VacA toxin or hepatitis C virus p7 protein, whichform hexameric channels and are considered to be important virulencefactors in the pathogenesis of peptic ulcer disease and HCV infection,respectively.

In a third aspect, the invention provides novel methods for makingcertain derivatives of β-CD. The introduction of an alkylamino group atthe primary position of β-cyclodextrins proved to be a challenge. Thedirect alkylation of per-iodo-β-cyclodextrin with an alcolatenucleophile (derived from an azidoalkanol for example) would pose someproblems since the basic alcolate may induce elimination orintramolecular substitutions. Nucleophilic displacement of iodide anionsfrom per-6-iodo-β-cyclodextrins, employing poor nucleophiles or elevatedtemperatures favors the intramolecular substitution reaction, resultingin the formation of 3,6-anhydro-D-glucopyranose residues within thestructure of per-6-iodo-β-cyclodextrin. Taking advantage of the highernucleophilicity of a sulfur atom over an oxygen atom, we utilized theintroduction of a sulfur atom at the primary position of theβ-cyclodextrin followed by a selective alkylation of the mercapto group,with a halogenopropionitrile to provide directly a precursor of thetarget compound 19. In this case, no supplementary protection anddeprotection steps are required.

Thus the invention provides an improved method for synthesizing asubstituted β-cyclodextrin, wherein the improvement comprisesintroducing a sulfur atom at the primary position of the β-cyclodextrinfollowed by a selective alkylation of the mercapto group, with ahalogenopropionitrile.

The following examples are intended to illustrate certain particularlypreferred embodiments of the invention and are not intended to limit thescope of the invention.

Example 1 Synthesis of β-cyclodextrin derivatives

Reagents. β-cyclodextrin derivatives 1-7 listed in Table 1 weresynthesized at Pinnacle Pharmaceuticals, Inc. (Charlottesville, Va.).Compounds 12 and 13 were purchased from Cytrea Ltd (Dublin, Ireland).Sulfo derivatives of β-cyclodextrin 8-11 were kindly provided by Dr.Gyula Vigh (Texas A&M University, College Station, Tex.). β-cyclodextrin14 was purchased from Sigma (St. Louis, Mo.). Most chemical reagentswere purchased from Aldrich Chemicals or Fisher Scientific and usedwithout further purification. Acetonitrile and dichloromethane weredistilled from CaH₂. DMF was distilled from CaH₂ under diminishedpressure. Triethylamine was distilled from P205.

Analysis. ¹H NMR and ¹³C NMR spectra were recorded on a General ElectricQE-300 or a Varian 300 spectrometer. Moisture sensitive reactions wereconducted under argon in oven-dried glassware. Analytical thin-layerchromatography was performed on Merk 60F₂₅₄ precoated silica gel plates.Visualization was performed by ultraviolet light and/or by staining withphosphomolybdic acid or sulfuric acid. Flash chromatography wasperformed using (40-60 μm) silica gel.

Synthesis. Cyclodextrins 2, 3, 4 and 5 were prepared according tostandard procedures.

(2-Phthalimidoethyl)isothiouronium hydrobromide (9). A suspension ofN-(2-bromoethyl)phthalimide (6) (3.0 g, 11.8 mmol) and thiourea (1.82 g,23.96 mmol) in absolute EtOH (5.7 mL) was stirred at reflux for 18 hafter which the product crystallized. After cooling to room temperaturethe product was collected by filtration, washing with small amounts ofchilled absolute EtOH and dried under vacuum. Compound 9 (4.0 g,quantitative yield) was obtained as colorless crystals; ¹H NMR (DMSO-d₆)δ 9.04 (brs, 2H), 7.91 (m, 2H); 7.11 (brs, 1H); 3.89 (t, J=5.8 Hz, 2H);3.52 (t, J=5.8 Hz, 2H).

(3-Phthalimidopropyl)isothiouronium hydrobromide (10). A suspension ofN-(3-bromopropyl)phthalimide (7) (3.0 g, 11 mmol) and thiourea (1.7 g,22.37 mmol) in absolute EtOH (5.3 mL) was stirred at reflux for 18 hafter which the product crystallized. After cooling to room temperaturethe product was collected by filtration, washing with small amounts ofchilled absolute EtOH (2×10 mL) and ether (10 mL) and dried undervacuum. Compound 10 (3.95 g, quantitative yield) was obtained ascolorless crystals. ¹H NMR (DMSO-d₆) δ 9.01 (brs, 2H), 7.90 (m, 2H);3.50 (t, J=6.2 Hz, 2H); 3.20 (t, J=6.6 Hz, 2H); 1.75 (m, 2H).

(4-Phthalimidobutyl)isothiouronium hydrobromide (11). A suspension ofN-(4-bromobutyl)phthalimide (8) (1.0 g, 3.5 mmol) and thiourea (540 mg,7.08 mmol) in absolute EtOH (1.7 mL) was stirred at reflux for 18 h. Theproduct did not crystallize as expected. However, upon cooling to roomtemperature, the syrupy mixture started crystallizing after a quickshaking and stirring. Ether (4 mL) was added and the mixture stirred for15 min. before collecting the product by filtration, washing with smallamounts of chilled EtOH. Compound 11 (1.22 g, 96%) was obtained ascolorless solid; ¹H NMR (DMSO-d₆) δ 9.02 (brs, 2H), 7.89 (m, 4H); 7.13(brs, 1H); 3.60 (t, J=6.4 Hz, 2H); 3.17 (t, J=6.6 Hz, 2H); 1.67 (m, 4H).

Heptakis (2,3-di-O-acetyl-6-deoxy-6-iodo)cyclomaltoheptaose (14). (SeeBaer et al., Carbohydr. Res. 228: 307 1992). To a solution ofper-6-iodo-β-cyclodextrin (2) (1.0 g, 0.52 mmol) in dry pyridine (5 mLwas added Ac₂O (7.5 mL) and a catalytic amount of DMAP (6.5 mg, 0.05mmol). The mixture was stirred at room temperature under argon for 48 h.The reaction was quenched by addition of MeOH (15 mL) and the solventsevaporated under diminished pressure. Coevaporation with small amountsof MeOH (3×4 mL) and toluene (3×4 mL) gave a brown residue, which waspurified on a silica gel column (20×3 cm). Elution with a gradientHexane-EtOAc (1:1 to 1:4) gave compound 14 (1.06 g, 81%) as a colorlesssolid, which crystallized upon trituration with diethyl ether; ¹H NMR(CDCl₃) δ 5.33 (brt, J=8.4 Hz, 1H); 5.2 (d, J=3.6 Hz, 1H); 4.83 (dd,J=3.9, 9.9 Hz, 1H); 3.58-3.81 (complex m, 4H); 2.09 (s, 3H); 2.05 (s,3H); mass spectrum (MALDI), calcd. for C₇₀H₉₁I₇NaO₄₂ m/z 2514.8 found2514.9 [M+Na] (100%).

Heptakis[2,3-di-O-acetyl-6-deoxy-6-(2-phthalimidoethyl)-thio]cyclomaltoheptaose(15). To a solution of heptakis(2,3-di-O-acetyl-6-deoxy-6-iodo)cyclomaltoheptaose (14) (0.5 g, 0.2mmol) and (2-phthalimidoethyl)isothiouronium hydrobromide (9) (0.99 g,3.0 mmol) in dry DMF (20 mL) was added Cs₂CO₃ (1.63 g, 5.0 mmol) and themixture stirred at room temperature under argon for 48 h. The mixturewas poured into ice (40 g) and 0.5 N HCl (200 mL) was added. The aqueouslayer was extracted with dichloromethane (3×50 mL). The combined organicphases were washed successively with 0.5 N HCl (200 mL) and brine (100mL), dried (MgSO₄) and evaporated under diminished pressure. The residuewas purified on a silica gel column (21×3 cm) eluting with EtOAc to givecompound 15 (145 mg, 23%) as a colorless solid. Another fraction (165mg) was obtained in a slightly impure form. ¹H NMR (CDCl₃) δ 7.73 (m,2H); 7.62 (m, 2H); 5.25 (t, 1H, J=8.7 Hz); 5.10 (brs, 1H); 4.80 (m, 1H);4.15 (m, 1H); 3.87 (t, 1H, J=8.4 Hz); 3.63 (m, 2H); 3.03 (m, 2H); 2.64(m, 2H); 2.05 (s, 3H); 2.01 (s, 3H).

Heptakis[2,3-di-O-acetyl-6-deoxy-6-(3-phthalimidopropyl)-thio]cyclomaltoheptaose(16). To a solution of heptakis(2,3-di-O-acetyl-6-deoxy-6-iodo)cyclomaltoheptaose (14) (250 mg, 0.1mmol) and (3-phthalimidopropyl) isothiouronium hydrobromide (10) (472mg, 1.37 mmol) in dry DMF (10 mL) was added Cs₂CO₃ (687 mg, 2.11 mmol)and the mixture stirred at room temperature under argon for 68 h. Themixture was poured into ice (50 g) and 0.5 N HCl (100 mL) was added. Theaqueous layer was extracted with dichloromethane (3×50 mL). The combinedorganic phases were washed successively with 0.5 N HCl (100 mL) andbrine (100 mL), dried (MgSO₄) and evaporated under diminished pressure.The residue was purified on a silica gel column (14×3 cm) eluting withEtOAc to give compound 15 (188 mg, 59%) as a colorless foam; ¹H-NMR (300MHz) δ 7.70 (dd, 2H, J=3.0 Hz, J=5.5 Hz); 7.58 (dd, 2H, J=3.1 Hz, J=5.4Hz); 5.23 (dd, 1H, J=8.3 Hz, J=9.6 Hz); 5.06 (d, 1H, J=3.8 Hz); 4.80(dd, 1H, J=3.8 Hz, J=9.7 Hz); 4.12 (m, 1H); 3.84 (t, 1H); 3.66 (t, 2H,J=6.9 Hz); 3.03 (m, 2H); 2.60 (m, 2H, J=5.9 Hz, J=12.9 Hz); 2.05 (s,3H); 2.02 (s, 3H); 1.91 (m, 2H; mass spectrum (MALDI), calcd. forC₁₄₇H₁₆₁N₇NaO₅₆S₇ m/z 3166.8 found 3166.8 [M+Na] (40%), 3168.8 (100%)and 3167.8 (80%).

Heptakis[2,3-di-O-acetyl-6-deoxy-6-(4-phthalimidobutyl)-thio]cyclomaltoheptaose(17). To a solution of heptakis(2,3-di-O-acetyl-6-deoxy-6-iodo)cyclomaltoheptaose (14) (404 mg, 0.16mmol) and (4-phthalimidobutyl) isothiouronium hydrobromide (11) (870 mg,2.42 mmol) in dry DMF (16 mL) was added Cs₂CO₃ (1.32 g, 4.04 mmol) andthe mixture stirred at room temperature under argon for 48 h. Themixture was poured into ice (50 g) and 0.5 N HCl (200 mL) was added. Theaqueous layer was extracted with dichloromethane (3×50 mL). The combinedorganic phases were washed successively with 0.5 N HCl (100 mL) andbrine (100 mL), dried (MgSO₄) and evaporated under diminished pressure.The residue was purified on a silica gel column (18×3 cm) eluting withEtOAc to give compound 17 (125 mg, 24%) as a colorless solid. Anotherfraction (132 mg) was obtained in a slightly impure form. ¹H-NMR (CDCl₃)δ 7.74 (m, 2H); 7.64 (m, 2H); 5.26 (m, 1H); 5.12 (d, 1H, J=3.6 Hz); 4.80(dd, 1H, J=3.7 Hz, J=9.8 Hz); 4.15 (m, 1H); 3.88 (m, 1H); 3.63 (m, 2H);3.03 (m, 2H); 2.65 (m, 2H); 2.06 (s, 3H); 2.02 (s, 3H); 1.73 (m, 2H);1.61 (m, 2H); mass spectrum (MALDI), calcd. for C₁₅₄H₁₇₅N₇NaO₅₆S₇ m/z3267.5 found 3267.3 [M+Na] (40%).

Per-6-(2-aminoethylthio)-β-cyclodextrin (18). A mixture of compound 15(100 mg, 31.92 μmol) and hydrazine monohydrate (1.55 mL, 31.92 mmol) inEtOH—H₂O 1:1 (1.5 mL) was stirred at 60° C. for 18 h. The solvents wereevaporated under diminished pressure to give a solid, which wassuspended in 1N HCl (5 mL) and stirred at rt for 8 h. The insolublematerial was filtered and the filtrate diluted with acetone (25 mL)until the product precipitated. The supernatant was removed bycentrifugation and the product washed with acetone (4×25 mL) and driedunder vacuum. The product 18 (46 mg, 89%) was obtained as a colorlesssolid. Mass spectrum (MALDI), calcd. for C₅₆H₁₀₅N₇O₂₈S₇ m/z 1548.9 found1548.8 [M] (100%).

Per-6-(3-aminopropylthio)-α-cyclodextrin (19). A mixture of compound 16(100 mg, 31.38 μmol) and hydrazine monohydrate (1.54 mL, 31.78 mmol) inEtOH—H₂O 1:1 (1.5 mL) was stirred at 60° C. for 16 h. The solvents wereevaporated under diminished pressure to give a solid, which wassuspended in 1N HCl (5 mL) and stirred at rt for 4 h. The insolublematerial was filtered and the filtrate diluted with acetone (25 mL)until the product precipitated. The supernatant was removed bycentrifugation and the product washed with acetone (4×25 mL) and driedunder vacuum. Compound 19 (53 mg, 85% yield) was obtained as a colorlesssolid. ¹³C-NMR (DMSO-d₆) δ 102.09, 84.52, 72.48, 72.23, 71.41, 37.79,33.03, 29.71, 26.85; mass spectrum (MALDI), calcd. for C₆₃H₁₁₉N₇NaO₂₈S₇m/z 1668.60 found 1668.82 [M+Na] (100%).

Per-6-(4-aminobutylthio)-β-cyclodextrin (20). A mixture of compound 17(80 mg, 25.31 μmol) and hydrazine monohydrate (1.22 mL, 25.31 mmol) inEtOH—H₂O 1:1 (1.2 mL) was stirred at 60° C. for 24 h. The solvents wereevaporated under diminished pressure to give a solid, which wassuspended in 1N HCl (5 mL) and stirred at rt for 4 h. The insolublematerial was filtered and the filtrate diluted with acetone (25 mL)until the product precipitated. The supernatant was removed bycentrifugation and the product washed with acetone (4×25 mL) and driedunder vacuum. The product 20 (40 mg, 94%) was obtained as a colorlesssolid. ¹³C-NMR (DMSO-d₆) δ 102.05, 84.43, 72.47, 72.22, 71.49, 38.40,32.85, 32.15, 26.12; mass spectrum (MALDI), calcd. for C₇₀H₁₃₃N₇O₂₈S₇m/z 1745.3 found 1745.9 [M+Na] (100%).

Example 2 Protection of Cells from Cytotoxicity

Recombinant B. anthracis lethal factor (rLF), edema factor (rEF), andprotective antigen (rPA) were acquired from List BiologicalLaboratories, Inc. (Campbell, Calif.). Murine RAW 264.7monocyte-macrophage cell line ATCC TIB-71 was obtained from AmericanType Culture Collection (Manassas, Va., USA). The cells were cultured inphenol free Dulbecco's Modification of Eagle's Medium/Ham's F-12 50/50Mix (Mediatech, Inc., Hermdon, Va., USA) supplemented with 10%heat-inactivated fetal bovine serum, 100 units/ml: 100 μg/mlpenicillin-streptomycin, 0.1 mM non-essential amino acids, and 0.5 mM2-mercaptoethanol at 37° C. in 5% CO₂. The cells were harvested usingCellstripper™ from Mediatech, Inc. and then were washed once with mediato remove the non-enzymatic dissociation solution. RAW 264.7 cells wereplated in 96-well flat-bottomed tissue culture plates from BectonDickinson (San Jose, Calif., USA) at a concentration of 10⁵ cells/wellin the DMEM medium mentioned above and incubated overnight at 37° C. in5% CO₂. RAW 264.7 cells were pre-incubated with different concentrationsof tested compounds in DMEM medium for 1 hr at 37° C. in a 5% CO₂atmosphere. Then DMEM medium or LeTx (LF=32 ng/ml; PA=500 ng/ml) in themedia were added, and the plate was incubated under the same conditionfor 4 hrs. Cell viability was estimated using a MTS kit from Promega(Madison, Wis., USA). A μ Quant spectrophotometer from Bio-TekInstruments, Inc. (Winooski, Vt., USA) was used to obtain OD₅₇₀readings.

Example 3 Inhibition of Ion Conductance

Ion conductance experiments were performed according to Montal andMueller [1,4] with modifications [15,16]. PA channels were reconstitutedinto planar lipid membranes formed from DPhPC; the membrane bathingsolution contained 0.1M KCl, 1 mM EDTA at pH 6.6. Ion conductancethrough PA channels was measured in the presence of PrAmBC.

1-3. (canceled)
 4. A method for inhibiting anthrax toxicity in a cell,comprising contacting the cell with a compound according to the formula

wherein R₂ is H, OH, OAc, OMe, or O(CH₂CH₂O)_(n); R₃ is H, OH, OAc, OMe,OSO₃Na, or NH₂; and R₆ is H, NH₂, SCH₂CH₂NH₂, SCH₂CH₂CH₂NH₂,SCH₂CH₂CH₂CH₂NH₂, I, N₃, SH, lower alkyl, S-alkylguanidyl,O-alkylguanidyl, S-aminoalkyl, O-aminoalkyl, aminoalkyl, aralkyl, aryl,heterocyclic ring(s), or OSO₃Na.
 5. The method according to claim 1,wherein R₆ is NH₂, SCH₂CH₂NH₂, SCH₂CH₂CH₂NH₂, or SCH₂CH₂CH₂CH₂ NH₂.
 6. Amethod for inhibiting anthrax toxicity in a cell, comprising contactingthe cell with a compound shown in FIG.
 1. 7. (canceled)
 8. A method forinhibiting anthrax toxin activity comprising administering a cycliccompound with a sevenfold symmetry and a diameter between 12 Å and 35 Å.9. A method for inhibiting a virulence factor that is a protein forminga trans-membrane channel with sevenfold symmetry for α-toxin of S.aureus comprising contacting a cell with a compound according to theformula

wherein R₂ is H, OH, OAc, OMe, or O(CH₂CH₂O)n; R₃ is H, OH, OAc, OMe,OSO₃Na, or NH₂; and R₆ is H, NH₂, SCH₂CH₂NH₂, SCH₂CH₂CH₂NH₂,SCH₂CH₂CH₂CH₂NH₂, I, N₃, SH, lower alkyl, S-alkylguanidyl,O-alkylguanidyl, S-aminoalkyl, O-aminoalkyl, aminoalkyl, aralkyl, aryl,heterocyclic ring(s), or OSO₃Na.
 10. The method according to claim 9,wherein R₆ is NH₂, SCH₂ CH₂NH₂, SCH₂CH₂CH₂NH₂, or SCH₂CH₂CH₂CH₂NH₂. 11.A method for inhibiting a virulence factor that is a protein forming atrans-membrane channel with sevenfold symmetry for α-toxin of S. aureuscomprising contacting a cell with a compound shown in FIG.
 1. 12. Amethod for inhibiting a virulence factor that is a protein forming atrans-membrane channel with sixfold symmetry for Heliobacter pylori VacA toxin comprising contacting a cell with a derivative of hexamericβ-cyclodextrin.
 13. A method for inhibiting a virulence factor that is aprotein forming a trans-membrane channel with sixfold symmetry forHepatitis C virus p7 protein comprising contacting a cell with aderivative of hexameric β-cyclodextrin.